Manufacture of coated fabric



Patented Feb. 18, 1947 MANUFACTURE OF COATED FABRIC Paul Rolland Austin, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application October 21, 1940, r Serial No. 362,169

1 Claim. (Cl. 117-76) This invention relates to improvements in coated products and coating processes, and more particularly to the provision of coatings upon nitro cellulose containing articles.

Conventional sheets, films or coatings consist- ,ing essentially of nitro-cellulose, or of nitro-cellulose compositions such as pyroxylin, as is Well known to the art, have pronounced flexibility and possess significant toughness, durability, and

abrasion resistance. When used as coatings for fabrics, the conventional ingredients of such compositions may be so adjusted, in known man- 'ners, as to facilitate whatever degree of penetration of the base fabric, or penetrational anchorage therein, may be desired. And yet, there are a number of fundamental faults in the surface qualities of the conventional nitro-cellulose pi'educts or coatings, for which faults, and in" spite of the vast amount of work that has been d a n in the art of coating flexible fabrics, the consuming public even up to the present time has not been provided with a wholly satisfactory solution. For instance, the nitro-cellulose coatings, per se, are subject, on aging, to brittleness, decomposition, fragility and separating from their base, as by cracking and peeling in consequence of exposure and weathering; and the tendency toward exudation to the surface, of softeners used in the said coatings, increases with rises in temperature, and has been a source of considerable difficulty in the past. In fact, for reasons such as these, it has come to pass that commercial nitrocellulose coated fabrics almost invariably are prepared with topcoats having different compositions from those of the main body of the nitrocellulose coating. Moreover, the usual topcoat not only differs from the main body of the coating in plasticizer and pigmentation, as a rule.

but often consists essentially of film-forming materials other than nitrocellulose, e. g., urea-formaldehyde resins or cellulose acetate. Such topcoats may serve various valuable functions, as by improving appearance, feel, surface hardness, and immunity to crocking; but hitherto it has been diflicult or impossible to attain these advantages without sacrificing other important ones. For instance, a suitably glossy surface is proneto be.

unduly brittle, orto have poor anchorage. Also, even with the toughest topcoats hitherto available, nitrocellulose coated fabrics have been unsatisfactory in applications where weakness or, brittleness of the topcoat isnot to be 'tplerated. Thus, glazed finishes employed in artificial patent leather characteristically are brittle, and tend to crack when repeatedly flexed, or when constricted in as'harp bend, as in the sewing of pleats, beading, and the like. Illustrations of such cracking and splitting often are encountered during the fabricationof handbags or'shoes, for iii-- stance, along lines of stitching or at points of sharp ,bend. Even if fabrication is completed without such cracking or splitting, early service failure brought about thereby isvery frequent. In this connection, it is to be observed, moreover, that when a topcoat is used which is more brittle than the base composition, cracking of the topin the aforesaid patents, but also coming within coat generally is accompanied by complete cracking through ,of the base composition, With'resultant exposure of the fabric backing; thus rendering the material unsatisfactory for further use,

This invention therefore has as an object the minimization or elimination of the aforesaid disadvantages inherent in products or coatings consisting essentially of nitro cellulose compositions, while at the same time preserving and utilizing the aforesaid advantageous properties thereof.

This object, as well as other important but subsidiary objects which will become apparent as the description of the invention proceeds, is ac-- complished according to the invention, by. apply ing to the nitro-cellulose containing base a coating consisting essentially of one or more synthetic linear polyamidesof types such as described in U. S. P. 2,071,250; 2,071,253; 2,130,523, and 2,130,948. It is to be observed, with regard to the structure of these polyamides that they contain amide groups i chain separating the amide groups is at least two..

Accordingly,in this specification and the claims appended thereto, the expression, synthetic linear polyamide, is to be understood as applying to polyamides not only belonging to types described the limitations pointed'out'in this paragraph.

I have discovered that when a layer of the said polyamides is applied over a nitro-cellulose surface, in accordance with procedures such as hereinafter set forth,.the adherence is a great even will survive satisfactorily a numberof hours ness in relatively high degree, as compared with ordinary lacquers and varnishes, substantially complete freedom fromtackiness even at extraordinarily high temperatures, and great strength, toughness, durability and flexibility.

The aforesaid polyamides characteristically can be formed into filaments which can be cold drawn into fibers showing molecular orientation along the fiber axis. The simple polyamides, i. e., those whichmay be derived from a single diamine'and dicarboxylic acid or from a single amino acid, exhibit as a rule high melting points, and solubility only in toxic or corrosive solvents such as in mineral acids, formic acid, and phenols. A number of'mor soluble polyamides are known, however, which also have increased compatibility with plasticizers, ascompared'with the simple polyamides. These polyamides include those prepared irom laterally substituted ingredients such as beta-methyl adipic acid, polyamides prepared from diamines and dibasic acids, one or both of which contain hetero'atoms of the oxygen family in the chain of atoms joining the amide-forming groups, and interpolyamides prepared from two different diamines and two different dibasic acids,

such asthat prepared from a mixture of hexa-- methylene diammonium adipate and'decamethylene diammonium sebacate. Polyamides of these types generally are more or less soluble in common organic solvents, rather'than merely in phenols, mineral acids, and formic and acetic acids. They also are soluble in certain unsaturated alcohols, and certain mixtures of alcohols withchlorinated hydrocarbons.

Still another series of interpolyamides are formed by the interpolymerization of at least one diamine. at least one dibasic acid, and at least one amino acid. They possess in large degree the strength, toughness, and durability characteristics of the simple polyamides, but are characterized further by their greater pliability and compatibility with modifying agents such as plas-' ticizers and resins, as well as by improved solubility in common nontoxic solvents, as for intives, e. g. caprolactam, sincethis interpolymer may be prepared from readily available ingredients, and possesses good tensile strength, flexibility, and compatibility.

The interpolyamlde prepared from 6 parts oi hex'amethylene diammonium adipate and 4 parts of B-aminocaproic acid, or an amide-forming derivative thereof, such as caprolactam or 6- aminocapronitrile, is particularly valuable, since it possesses good solubility in relatively non-toxic and non-corrosive aqueous alcohol mixtures, and melts at the relatively low temperature of 165-175 C. While this temperature is sumciently high to obviate tackiness in ordinary use, it still is low enough to permit certain important fabricating steps,-such as the embossing of coated fabrics. The invention therefore will be describ with particular reference to this interpolymer, though it is to be understood that the description will differ only in details, as regards the carrying out of the invention with.other polyamides. The coatings may be applied over the nitrocellulose base in a number of ways. method consists in applying a solution of the polyamide onto the base and removing the solvent therefrom by means of evaporation. Thus, in the case of the preferred interpolyamide, a mixture of parts by weight of ethanol and 25 parts by weight of water may be used as a solvent, and the solution conveniently may be applied to the base in conventional industrial coating equipment. An advantage of the solvent coating method of applying the coating is that surface gloss often may be controlled not only by varying the composition of the coating, but also by varying the method of application. For instance, when the preferred interpolymer is applied from an ethanol-water solution, a high gloss may be obtained by applying thin coats and drying at elevated temperatures, while dull finish products may be obtained by applying thicker coats and allowing them to dry more slowly.

Another convenient method for applying polyamide coatings consists in applying an emulsi or dispersion of the polyamide composition to t e nitro-cellulose base and subsequently removing the vehicle by evaporation. Still another metlifiii consists in laminating a preformed sheetof polyp amide composition onto the nitro-cellulose base by means of heat, pressure and, if desired, an adhesive. Another method which 'is particularly suitable in the case of low melting polyamide compositions consists in melt coating of the hitro-cellulose base, as by dipping, spraying, or

extruding a film-,of molten polyamide composition ExampZeI A solution of polyhexamethylene adipamide in.

formic acid is applied to a film consisting of nitrocellulose containing 25% of camphor, as plasticizer. The adhesion of the residual polyamide coating to the nitrocellulose,after removal of the solvent, is excellent, even after 16 hours soaking in water.

Example II Duplication of Example I, except for the employment, in place of polyhexamethylene adipamide, of an interpolyamide prepared by the interpolymerization of a mixture of equirnolecular amounts of hexamethylene diammonium adipate A convenient,

and decamethylene diammonium sebacate, yields the same results in Example I, insofar as the excellence of adherence to the nitrocellulose is concerned.

' Example III summer weather with the polyamide coating facing thesouth at an angle of 45 from' the horizontal, the polyamide coating retains its good adhesion and shows no apparent failure.

Example IV A mixture of'2.25 parts of amylb'enze'nesulfon amide, 30 parts of a solvent mixture comprising 2 volumes of methanol and 1 volumeof trichloroethylene, 'and 5.52 parts of an interpolyamide having a melt viscosity of 1419 poises at 250 C., which is prepared by the interpol'ymeriz ation of a mixture of 60 parts of hexamethylene diammonium adipate and 4.0 parts of omega-amino 5 capronitrile, is heated and stirred to homogeneity under reflux at 55-60" C. for 11 hours. This solution then is applied over a pyroxylin coated fabric which consists of a 1.12--53",sateen carrying 14 oz.. per linear yard of 50" width of a coating composition comprising a mixture of nitrocellulose, a plasticizer therefor, and a pigment "gontaining carbon black. This typeand weightof coating is well known to the, art. The above-described polyamide topcoating solution is applied to the nitrocellulose coated fabric in commercial fabric coating equipment, by applying the solution to coated fabric, conveying the mass under a doctor knifeso arranged as to spreada thin film of the solution evenly over the nitrocellulosev coated fabric, and subsequently drying the coated fabric by passing itthrough a drying oven. The rate of application of coating is yards/min, and the temperature of the drying oven is 180 F. The drying oven is feet long. Three coats are applied in this man-. ner, and about 0.5 oz. of the polyamidetopcoat (based on non-volatile ingredients) is thus applied'to each linear yard of the coated fabric which is in width after coating. The product is found to havegreatly improve gloss and toughness, and the anchorage oi. the

nitrocellulose'to the polyamide topcoat is good. A sample of the product withstands 7500 flexes in a Schiltknecht flexing machine, such as described in Automotive Industries '49, 1262-6; whereas a sample of the untopcoated nitrocellulose coated materialfails by cracking after 2000 such flexes. V

A number of sandal-type slippers havingpleated Vamps are prepared from the product, together with samples for comparison from the untopcoated pyroxylin coated fabric and from Similar pyroxylin coated fabric carrying a commercially used topcoat comprising a urea-formaldehyde resin. Whereas there is considerable cracking and splitting of the two last-mentioned compositions, especially in areas of sharp bending, as across the pleated vamp, the polyamide topcoated pyroxylin coated fabric withstands this fabrication perfectly. Furthermore, the polyamide topcoated material is superior-in service durability, the 'untopcoated and the urea-formaldehyde resin topcoated materials tending to fail 5 rapidly'by cracking inthose areas which are subjected to repeated flexing. v

Ladies handbags also are prepared from the product of this example. As compared with present commercial pyroxylin coated fabric, the new material is markedly-superior in its resistance to cracking and splitting along lines of stitching and sharp bending. The products are of attractive appearanceand feel, and are not marred, scuffed,

' or otherwise injured after several months of use;

Example V A polyamide topcoating solution similar tothat described in Example IV is applied in the same manner as described therein to "a base material under this treatment. I I

' I Example V1 Interpolyamide'prepared from parts of hexa methylene diammonium adipate and 40 parts of caprolactam, and having a melt viscosity of 1188 poises at 250 C. is used. A solution of 23 parts ofthis polymer in 77 parts' of a solvent comprising a mixture of 8 volumes of. ethanol and 2 volumes of water is applied as a topcoat'of;

pyroxylin coated fabric similar to that described in Example IV. During the application, the solution is maintained at a temperature as low as 1 40 0., thefabric is preheated to only 60 0.,

topcoat is.well anchoredto the base. uct has-better resistance to cracking and flexing so than either the'untopcoated material or similar methoxybenzamide, 0.75-part of the oil-solublev resinous reaction product of formaldehyde with p-hydroxydiphenyl, 23.1 parts of ethanol, 8 parts 60 of methyl Cellosolve, and'lfl parts of water, This solution is appliedas a topcoat over pyroxylin coatedmaterial" similar to that described in Example IV. The product has a hard, extremely glossy surface, and the topcoat is Well anchored tothe nitrocellulose. .The resistance of the prod-' uct-to cracking upon repeated bending'is markedly improved by theipresence of the topcoating.

? Example VBIII An interpolyamide is prepared by interpoly-' merization of 40 parts of hexamethylene diam monium adipate, 15 parts of hexamethylenedi ammonium sebacate, andf45par'ts of omegaamino-caproic acid. A solution-then is prepared. contains 65-. parts of this interpolymer, 2 l

which which comprises 1.12-53" sateen coated .to' a 1 untreated base. material cracks and splits badly and the solventevaporates from the product at 60 C. The producthas a highgloss. and the The .prodmaterial carrying acurrent commercial topcoat,

parts of diphenyloloctadecane:and'il parts of a condensation product of propylene glycol with,

castor oil, dissolvedat 20% solids'in asolvent mixture comprising equal ,volumes of chloroform and methanol;- This solution is used to coat nitrocellulose coated fabric similar to that. described in ExampleIV, twocoats of thesolution being applied, and the solvent being allowed to evaporate at room temperature. The polyamide Ii such a topcoat is applied very thin,"'it"largely topcoat is well anchored, and the product has an attractive dullisatiny surface. The product is verytough and pliable and has good sewing ;char-: 'acteristics.

In a similar manner anexcellent fabric was obtained by applying to a nitrocellulose coated fabric .a topcoating of interpolyamide derived from 40 parts of hexamethylene diammonium adipate, 30 parts of hexamethylene diammonium sebacate, and 30 parts of: caprolactam plasticized with a mixture of-1,12-diphenyloloctadecane and butyl phthalyl butyl glycolate', using as solvent a mixture-of 96% ethanol and "water in a 90:10 ratio by volume. q l I ExamplcIX An interpolyamide is'preparedl from 262 parts I or hexamethylene diam'monium adlpate and 374 parts of decamethylenediammonium sebacate.

coat composition containing the preferred inter-.- polymer dissolved in ethanol-water, is applied over'an embossed base, the topcoatsolution will be thicker in the valleys, thus bringing about a gloss differential, the high spots being glossy and the valleys being dull. It hitherto has been necessary to apply several successive coats of different compositions, in order to achieve such effects- When it is desired to prepare a product of ex -H tremely high glass, the glossof the polyamid coating or topcoating may be improved by ap-.

plying to it a final wash with'a polyaniide solvent, such as an alcohol or an alcohol-water mix ture. Frequently it is advantageous, in orderfur ther to improve the gloss, to incorporate in such a solvent wash a small amount of a relatively high Thus, in the case boiling solvent type material. of the preferred interpolyamide, which is soluble ina '75:25'welght mixture of ethanol and water, the gloss is improved by washing coatings containing this material with a solvent mixture comprising a 50:30:20 weight mixture of ethanolz' methylCellosolv'e:water. The use of this mixture,'or' of similar mixtures, as the actual solvent- 7 in the application of the polyamide coating, also A solution of :this interpolmer in a; mixture of methanolfchloroform, and n-butanolfis applied as a. topcoat over nitrocellulose coated fabric similar to um described in Example 1v, allowing the solvent to evaporate at room temperature.

I The topcoat is clear and glossy.

Example). .r

r polyesteramide is prepared from 15 parts of 'hexamethylene diammonium adipate and 85 parts of an equimolar mixture of ethylene glycol f and adipic acid. A solution oil this polyestera'mide,'at 33% solids in a solvent'mixture comprising 'l volumes off-toluene'and 3volumes of benzene-denatured ethanol, is 'appliedas atop- ,coat over-the type of pyrcxylinicoated sheeting which is in common useias'bo'okbinding material; The product has good anchorage and-an attractive glossy 'appearance.1-' i -1 i Y The polyamide coating maybe applied to the nitrocellulose base either before or after embossing of'the-latter. If the application of the coating is carried outprior' tof embossing, the

product may be embossed thereafter, with the aid of standard embossing plates or rolls; Nu-

merous decorative effectsare to' be' achieved,

howeven by applyingthe'polyan'iide coating after embossing of the base. Thus, in the caseoi' an embossed -pyroxy1in" coated fabric, attractive color eflectsmay be obtained by pigmenting the results i an improvement in gloss and brilliance,

and hence frequently isadvantageous, although the presence of a relatively non-solvent suchas methyl Cellosolve generally causes the solutions to gel somewhat-more rapidly than otherwise, at room temperature. i Y

Suitable pol'yamide's, in addition, to those already particularized hereinabove, include those formedrby the reaction of a diaminewith a substantially equimolecular amount of dibasic acid or amide-forming derivative thereof, such asan V ester,'halide,' amide, or anhydride. There may!" be mentioned, furthermore, polyamides formecL from polymerizable amino acids of the type; Rr--NH'R COOR, where R'.is a divalent crj ganic radical and His a uniyalent organic radical or hydrogen. Interpolymers derived fro'm mixtures of the above ingredients also are very valuable, an especially valuable'subclas's, typified in the foregoing examples, being. those interpoly mers derived by interpoly'merization of an equi- I polyamide coating with acoloror shade-which is j j diil'erent. from that inthe 'py'roxylinbase coat.

- accumulates'in the valleys of'tne grain base coat,

. beingsubstantially wiped ofith'e high spots by the action or the spreading knife. There ,thus

will result a product wherein the high spots carry the amidessoluble 'injalcohol-water mixtures dry dull, whereas thin coatingseof identical composition gi'veja glossy finish. "Thus, if'isuch an unpi'g-a 1 merited 'polyamlde topcoat, as for instance a topcolor of the base'co'at; while the valleys carry the'c'ontrasting color'of the topcoatl' One of the most preferred embodiments-of the invention takes; advantage of the fact, which already has been referred to hereinabovc, that relatively 'thiclr polyamide coatings of interpoly- Iable amino acid or derivative thereof.

molecular, mixture of a straight chain diamine and a straight chain dibasic acid, which mixture also contains anydesired amount of a polymeriz amines suitable for use may be'mentioned tetra-, penta-, hexa-, octa-, and decamethylene diamines. as well as substituted derivatives such as 3-methyl hexamethylene diamine, diaminoisopropanol, and aromatic diamines such as mphenylen'e, diamine, As suitable dibasic acids may be mentioned 'malonic, glutaric, adipic, plmelic, suberic, sebacic acids and their substituted derivatives, such as methyl adipic acid.

"f"""Also operable are amide-forming derivatives of these acids, such as esters, halides, amide, and 'anhydrides. Furthermore, as polyamide-forming ingredients, either alone or in admixture with the above-mentioned diamines and dibasic acids,

- there may be used 'polymerizable amino acids lactams.

As di- I less they have an intrinsic viscosity above 0.4,

w ere intrinsic viscosity is defined as in U. S. P. 2,130,948, coatings produced with several of the three or more component interpolyamides or interpolyester-amides will be found satisfactory for some purposes, even though the intrinsic viscosity of the particular interpolyamide be less than 0.4.

Polyamides having an intrinsic viscosity between 0.6 and 2.0 are particularly suitable for use on e. g. N-beta-hydroxyethyl-o-methoxybenzamicle.

Among other plasticizers suitable for use in tlg polyamide coatings and of especial value in the case of the preferred polyamide interpolymers specified in the examples, may be mentioned N- thylamylbenzenesulfonamide; phenols such as diphenyloloctadecane and octyl phenol; salicylarnides; and the known softeners for the polyamides, mixed, if desired, with other materials of known softening action for the polyamides or nitrocellulose, such as cast-or oil or derivatives thereof, high boiling aromatic or aliphatic esters. and the like. Pigments, fillers and flatting agents also may be incorporated in the coatings.

The coating compositions also may includeresinous materials,.waxes and other modifying agents, whether or not compatible with the polyamides. Thus, the oil-soluble types of phenolformaldehyde resins are of especial value in contributing gloss, luster and hardness to the composition, while finely divided incompatible resins or cellulose derivatives such as cellulose acetate, are of value as fiatting agents. Diatomaceous earth and aluminum stearate can also be used as fiatting agents.

The choice of solvents to be used in the solvent application of the polyamide coatin s will depend upon the nature of the particular polyamide which is to be applied. Thus. formic and acetic acids are general solvents for the polyamides, while certain of the polyamide interpolymers may be dissolved in alcohols such as n-butanol, or unsaturated alcohols, or in mixtures of alcohols and chlorinated hydrocarbons, e.. g., mixtures -of methanol and chloroform, or in alcohol-water mixtures. In general, any liquid or mixture of liquids which is a solvent for the polyamide may be used, although where possible it is preferred, for ease of recovery, to select liquids which boil between 40 C. and 150 C.

The nitrocellulose coated fabrics coated according to the process of the invention are, in general, those which are known to the art.

The nitrocellulose undercoating usuallywill contain auxiliary ingredients, e. g., plasticizers, pigments,.stabilizers, or the like; and may, if desired, be modified with resins, drying oils, and so forth. The flexible sheet materials carrying the nitrocellulose coating generally will be fabrics such as cotton sheetings, sateenspand twills. Fabrics formed of materials other than cotton,

however, as for instance silk, rayon, nylon, and

wool, also may'be used. Knitted or felted constructions also may be used.

The relative amounts of nitrocellulose-containing undercoat and of polyamide-containing topcoat may be varied as desired. In the case of the nitrocellulose-eontaining undercoat, however, it ordinarily is preferred to apply. a weight of coating at least equal to 1.5 oz. per linear yard of 50" width, since lighter weights are generally insufiicient to cover the fabric, and give products of rather poor durability. Coating weights in excess of 30 oz./50" yard are not recommended,

since heavier coatings often give products that are undesirably stiff. It generally is desirable to apply a relatively thin polyamide topcoat, a coating weight of 0.1-2.0 02/50" yard being especially satisfactory.

Another use of this invention is in coating a nitrocellulose film with polyamide for use as a photographic film base. The polyamide coating serves to reduce the fire hazard and increase the life of the film in service. e. g.. in a proiector.

The products of this invention possess advantages in toughness. durability, appearance. and surface characteristics which render them distinctly superior to present commercial nitrocellulose products. In particular. the fabric-nitrocellulose primer coat-polyamide toocoat products of the invention are of especial value in applications where toughness is required; such as in upholstery material and shoe upper material,

especially in the ease of full vamp shoes.

,As many apparently widely different embodiments of t is invention maybe mad without departing from the spirit and scope thereof, it

is to be understood that I do not limit myself- REFERENCES CITED The following references are file of this patent:

UNITED STATES PATENTS Number Name Date 2,216,735 Carothers Oct. 8, 1940 1,951,119 Alt Mar. 13, 1934 2 227,843 Quenelle Jan. 'I, 1941 2,071,250 Carothers Feb. 16, 1937 1,954,750 Hopkins Apr. 10, 1934 2,260,024 Hall Oct. 21, 1941 2,188,332 Carothers Jan. 30, 1940 which are of record in the 

